Secure integrated-circuit systems

ABSTRACT

A method of making a secure integrated-circuit system comprises providing a first integrated circuit in a first die having a first die size and providing a second integrated circuit in a second die. The second die size is smaller than the first die size. The second die is transfer printed onto the first die and connected to the first integrated circuit, forming a compound die. The compound die is packaged. The second integrated circuit is operable to monitor the operation of the first integrated circuit and provides a monitor signal responsive to the operation of the first integrated circuit. The first integrated circuit can be constructed in an insecure facility and the second integrated circuit can be constructed in a secure facility.

PRIORITY APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/795,313, filed on Jan. 22, 2019, the disclosure ofwhich is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to structures and methods forsecure hardware systems incorporating small monitor integrated circuits.

BACKGROUND

Electronic and photonic systems typically employ many differentcomponents supplied from a wide variety of sources in many differentcountries. Such diverse sources can be difficult to manage and secure toensure that every component is constructed to specification by amanufacturer of the end system. For example, a hardware system caninadvertently incorporate malicious circuitry. Exhaustively testingevery component at every stage of construction and integration can bedifficult and prohibitively expensive. By interrupting the technologysupply chain in some fashion, inimical actors can compromise thesecurity and performance of electronic or photonic systems, for exampleby inserting undesirable and malicious circuitry into a system or bycovertly redesigning components that are then employed in a compromisedsystem. Such compromised systems can be accessed to retrieve informationor to inhibit the performance of the compromised systems.

Monitor circuits for establishing appropriate operation are sometimesused to ensure that a circuit is operating as desired. Such monitorcircuits typically provide a monitor signal when the circuit operationis no longer within specification. For example, power systems caninclude monitor circuits to ensure that the power supplied meets thedesired specifications. Circuits for checking bit errors incommunication systems are used to detect and correct such errors.However, such systems typically require relatively large monitorcircuits that are not readily integrated into a small system.

There is a need, therefore, for systems, structures, devices, andmethods that provide secure hardware systems where components of thehardware system are not under the complete control of the hardwaresystem manufacturer.

SUMMARY

The present disclosure provides, inter alia, structures, materials, andmethods that provide secure hardware systems, for example wherecomponents of the hardware system are not under the complete control ofthe hardware system manufacturer.

According to some embodiments, a method of making a secureintegrated-circuit system comprises providing a first integrated circuitin a first die having a first die size and providing a second integratedcircuit in a second die. The second die size is smaller than the firstdie size. The second die is transfer printed onto the first die andconnected to the first integrated circuit, forming a compound die. Thecompound die is packaged. The second integrated circuit monitors theoperation of the first integrated circuit and provides a monitor signalresponsive to the operation of the first integrated circuit. The firstintegrated circuit can be constructed in an insecure facility and thesecond integrated circuit in a secure facility.

According to some embodiments, the first die has an area that is ten,twenty, fifty, one hundred, two hundred and fifty, five hundred, onethousand, five thousand, ten thousand times, one hundred thousand times,one million times, one hundred million times, one billion times, orlarger than an area of the second die. According to some embodiments,the second die has a length and a width that are both less than or equalto 200 microns, 100 microns, 50 microns, 25 microns, or 10 microns.

The second die can comprise at least a portion of a fractured orseparated tether.

According to some embodiments, connecting the second integrated circuitto the first integrated circuit comprises photolithographically formingwires electrically connecting the second integrated circuit to the firstintegrated circuit. According to some embodiments, the second diecomprises one or more connection posts and the first integrated circuitis connected to the second integrated circuit through the one or moreconnection posts by the step of micro-transfer printing. According tosome embodiments, connecting the second integrated circuit to the firstintegrated circuit comprises wire bonding the second integrated circuitto the first integrated circuit.

According to some embodiments, the connection is an electrical, optical,or electro-optic connection. According to some embodiments, the packagecomprises a cavity and the step of packaging the compound die comprisesdisposing the compound die in the cavity. According to some embodiments,the package comprises package leads and the step of packaging thecompound die comprises connecting the package leads to the compound die.According to some embodiments, the step of packaging the compound diecomprises wire bonding the first integrated circuit to one or more ofthe package leads. According to some embodiments, the step of packagingthe compound die comprises wire bonding the second integrated circuit toone or more of the package leads.

Some embodiments comprise encapsulating the compound die and thecompound die is encapsulated, for example with an organic or inorganicdielectric material, such as a resin, an oxide such as silicon dioxide,or a nitride such as silicon nitride.

Some methods comprise providing a plurality of first dies, providing aplurality of second dies, and micro-transfer printing each second die ofthe plurality of second dies onto a first die. Some methods comprisemicro-transfer printing multiple second dies in a common step. Somemethods comprise micro-transfer printing only one second die onto eachfirst die. Some methods comprise micro-transfer printing multiple seconddies onto each first die. Some methods comprise providing multiplesource wafers each having a plurality of second dies and micro-transferprinting a second die from each second wafer onto a common first die.Some methods comprise connecting each second integrated circuit on acommon first die together.

According to some embodiments, a secure integrated-circuit systemcomprises a first integrated circuit in a first die having a first diesize and a second integrated circuit in a second die having a second diesize smaller than the first die size. The second integrated circuit isoperable to monitor the operation of the first integrated circuit and toprovide a monitor signal responsive to the operation of the firstintegrated circuit. The second die is non-native to the first die andthe second die can be micro-transfer printed from a source wafer to thefirst die. The first die can be provided in a destination wafer ordestination substrate. The second integrated circuit is connected to thefirst integrated circuit, such that the first die and the second dietogether form a compound die. The compound die is disposed in a package.

According to some embodiments, the second die comprises a fractured orseparated tether. Two or more second dies can be disposed on a commonfirst die, the two or more second dies connected together to form amonitor circuit.

According to some embodiments, the first integrated circuit isconstructed in an insecure facility. The first integrated circuit canincorporate a malicious circuit. The second integrated circuit can beconstructed in a secure facility.

According to some embodiments, the first die has an area that is atleast ten, (e.g., at least twenty, at least fifty, at least one hundred,at least two hundred and fifty, at least five hundred, at least onethousand, at least five thousand, at least ten thousand times, at leastone hundred thousand times, at least one million times, at least onehundred million times, or at least one billion times larger than an areaof the second die (e.g., and no more than one hundred thousand timeslarger, no more than one million times, no more than one hundred milliontimes, no more than one billion times larger than the area of the seconddie). The second die can have a length and a width that are both no morethan 200 microns (e.g., no more than 100 microns, no more than 50microns, no more than 25 microns, or no more than 10 microns).

According to some embodiments, the second integrated circuit isconnected to the first integrated circuit by one or more of anelectrical connection, an optical connection, and an electro-opticconnection. According to some embodiments, the second integrated circuitis electrically connected to the first integrated circuit with at leastone wire bond, one surface wire, or one connection post.

In some embodiments, the components are computers, servers, orcommunications devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects, features, and advantages ofthe present disclosure will become more apparent and better understoodby referring to the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a flow diagram according to illustrative embodiments of thepresent disclosure;

FIG. 2 is a flow diagram according to illustrative embodiments of thepresent disclosure;

FIG. 3 is a perspective of components useful in various embodiments ofthe present disclosure;

FIG. 4A is a perspective and FIG. 4B is a schematic cross section takenalong cross section line A of FIG. 4A of a stamp and source waferaccording to illustrative embodiments of the present disclosure;

FIG. 5 is a schematic cross section of the stamp in contact with asubset of second dies on the source wafer according to illustrativeembodiments of the present disclosure;

FIG. 6A is a perspective and FIG. 6B is a schematic cross section takenalong cross section line A of FIG. 6A of the stamp with the subset ofsecond dies removed from the source wafer according to illustrativeembodiments of the present disclosure;

FIG. 7A is a perspective and FIG. 7B is a schematic cross section takenalong cross section line A of FIG. 7A of the stamp before micro-transferprinting the subset of second dies from the stamp onto first dies on adestination wafer to form a compound die according to illustrativeembodiments of the present disclosure;

FIG. 8A is a perspective and FIG. 8B is a schematic cross section takenalong cross section line A of FIG. 8A of compound dies according toillustrative embodiments of the present disclosure;

FIG. 9 is a schematic cross section of compound dies with bond wiresaccording to illustrative embodiments of the present disclosure;

FIG. 10 is a schematic cross section with photolithographically definedconnections according to illustrative embodiments of the presentdisclosure; and

FIG. 11 is a schematic cross section with connection posts according toillustrative embodiments of the present disclosure.

FIG. 12 is a perspective of a compound die in a package according toillustrative embodiments of the present disclosure;

FIG. 13 is a schematic cross section of compound dies with bond wiresand connection posts according to illustrative embodiments of thepresent disclosure;

FIG. 14 is a schematic cross section of compound dies with bond wiresaccording to illustrative embodiments of the present disclosure;

FIG. 15 is a schematic cross section of compound dies with bond wiresaccording to illustrative embodiments of the present disclosure; and

FIG. 16 is a schematic illustrating the operation of compound diesaccording to illustrative embodiments of the present disclosure.

The perspectives shown in FIGS. 3A, 6A, and 7A are explodedillustrations with exaggerated viewing angles and the two cross sectionlines A indicated in some of the perspective Figures are actuallycongruent.

Features and advantages of the present disclosure will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The figures are not necessarilydrawn to scale.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Certain embodiments of the present disclosure are directed towardmethods and structures for providing secure hardware systems when atleast some component of the hardware system is constructed or providedin an insecure facility and can incorporate malicious circuitry.

The flow diagrams of FIGS. 1 and 2 and the sequential cross sections andperspectives of FIGS. 3-8 illustrate methods and structures of someembodiments. Referring specifically to FIG. 3, a method of making asecure integrated-circuit system according to some embodiments compriseproviding a first integrated circuit 21 in or on a first die 20 having afirst die size in step 100. A plurality of first dies 20 each with firstintegrated circuits 21 can be provided in a destination wafer 40. Firstintegrated circuit 21 in or on first die 20 can be constructed in aninsecure facility. In step 110, a second integrated circuit 23 isprovided in or on a second die 22 having a second die size smaller thanthe first die size. Second integrated circuit 23 can be a monitorcircuit. Second integrated circuit 23 can be constructed in a securefacility (e.g., when first integrated circuit 21 is constructed in aninsecure facility). First and second integrated circuits 21, 23 can bemade in first and second dies 20, 22, respectively, usingphotolithographic methods and materials. A plurality of second dies 22each with second integrated circuits 23 can be provided in a sourcewafer 10. In some embodiments, multiple source wafers 10 are providedeach with different second dies 22 comprising different secondintegrated circuits 23 and multiple, different second dies 22 aredisposed on a common first die 20. In step 120, a package 90 isprovided. Optionally, a stamp 30 with stamp posts 32 each with a stamppost area on a distal end of each stamp post 32 is provided for use inmicro-transfer printing, for example micro-transfer printing second dies22 onto first dies 20 or into package 90.

In step 130, second die 22 is transfer printed (for examplemicro-transfer printed using stamp 30) onto first die 20 and secondintegrated circuit 23 is connected to first integrated circuit 21, toprovide a compound die 60. Optionally, second integrated circuit 23 canbe connected to first integrated circuit 21 by the step 130 of transferprinting second die 22 onto first die 20 (as represented in FIG. 1 withcombined step 135) or can be connected after transfer printing seconddie 22 onto first die 20 (as shown in step 140 of FIG. 1), for exampleusing photolithographic or wire bonding materials and methods (see, forexample, FIGS. 9-11 and 13-15, discussed further below). Compound die 60is then packaged, for example with a plastic or ceramic package 90(e.g., as shown in FIG. 12, discussed below) as are commonly used in theintegrated circuit industry. A package 90 is a container that containscompound die 60 and, in some embodiments, provides connections, forexample with package leads 94, to first and second integrated circuits21, 23. As shown in FIG. 2, in some embodiments, second integratedcircuit 23 can be connected to first integrated circuit 21 afterpackaging in step 141 (as shown in FIG. 2), rather than before packaging(as shown in FIG. 1).

In operation, second integrated circuit 23 monitors the behavior offirst integrated circuit 21 and provides a monitor signal 74 (see, forexample, FIG. 16, discussed further below) responsive to any combinationof the behavior, performance, or operation of first integrated circuit21 that is undesired. Monitor signal 74 can be electronic, optical, orcan use other communication modalities and energy types. According tosome embodiments, first integrated circuit 21 inadvertently incorporatesundesired malicious circuitry when first integrated circuit 21 isconstructed in an insecure facility. A malicious circuit can be anundesired circuit provided in first integrated circuit 21 that purposelyperforms functions or operates in a way that is deleterious ordisruptive to the desired function of or interferes with a secureintegrated-circuit system 99 (e.g., shown in FIG. 12) incorporatingfirst integrated-circuit 21.

The sequential cross sections and perspectives of FIGS. 4A-9, illustratein more detail a method of transfer printing (step 130) second die 22onto first die 20, according to some embodiments of the presentdisclosure. Referring to the exploded FIG. 4A perspective andcorresponding cross section FIG. 4B taken along cross section line A ofFIG. 4A, stamp posts 32 protrude from stamp 30 to contact second dies 22when stamp 30 is pressed against second dies 22, for example using anopto-mechatronic motion platform and control system. As shown in FIG.4B, second dies 22 are entirely disposed over, and can be formed on,sacrificial portions 14 spatially separated by anchors 50 in sacrificiallayer 11 of source wafer 10. Sacrificial layer 11 can be a patternedsacrificial layer 11 or an anisotropically etchable layer of sourcewafer 10. For example, second dies 22 can be, but are not necessarily,arranged in a rectangular array, for example in a regulartwo-dimensional array, as shown in FIG. 4A. A dielectric layer 54disposed over source wafer 10 and sacrificial portions 14 connects eachsecond die 22 with a tether 52 to an anchor 50. In some embodiments, oneor more tethers 52 connect a second die 22 to each of one or moreanchors 50. Tethers 52 can be laterally connected to anchors 50 (e.g.,as shown) or disposed in other locations, for example beneath seconddies 22. In some embodiments, first dies 20 are also provided on asource wafer and transferred to a package 90 (e.g., before or after (i)second dies 22 are transferred to first dies 20 and/or (ii) firstintegrated circuits 21 are electrically connected to second integratedcircuits 23).

Referring to FIG. 5, sacrificial portions 14 (shown in FIG. 4B) aresacrificed, for example by etching sacrificial portions 14 to form gaps16, so that second dies 22 are suspended over gaps 16 and attached toanchors 50 of source wafer 10 by tethers 52 that maintain the physicalposition of second dies 22 with respect to source wafer 10 aftersacrificial portions 14 are etched. Stamp 30 is moved into position withrespect to source wafer 10, for example by an opto-mechatronic motionplatform, and second dies 22 are picked up from source wafer 10 byadhering second dies 22 to stamp 30, for example by pressing stamp 30against second dies 22 on source wafer 10 with the motion platform andadhering second dies 22 to the distal ends of stamp posts 32, forexample with van der Waals or electrostatic forces.

As shown in the FIG. 6A perspective and FIG. 6B cross section takenalong cross section line A of FIG. 6A, stamp 30 in contact with seconddies 22 suspended over gaps 16 is then removed from source wafer 10 bythe motion platform, separating or fracturing dielectric layer 54tethers 52 from anchors 50 to form separated or fractured tethers 53,respectively, and picking up second dies 22 from source wafer 10 withstamp 30, providing picked-up second dies 22 on stamp posts 32 of stamp30. Picked-up second dies 22 can comprise a separated or fracturedtether 53.

Referring to the perspective of FIG. 7A and cross section of FIG. 7Btaken along cross section line A of FIG. 7A, stamp 30 and second dies 22on stamp posts 32 of stamp 30 with fractured tethers 53 are moved intoposition and aligned with respect to destination wafer 40.

Referring to the perspective of FIG. 8A and cross section of FIG. 8Btaken along cross section line A of FIG. 8A, picked-up second dies 22 onstamp 30 with fractured tethers 53 are micro-transfer printed to firstdies 20 on or in destination wafer 40 with stamp 30, and stamp 30 isremoved. As shown in FIGS. 4A-8B, each of multiple stamp posts 32 ofstamp 30 can pick up a second die 22 and transfer print it to a firstdie 20 of destination wafer 40, so that multiple second dies 22 aretransfer printed to corresponding multiple first dies 20 in eachtransfer print operation.

After second dies 22 are transfer printed onto first dies 20 (step 130),second integrated circuits 23 formed in second dies 22 are eachconnected to a first integrated circuit 21 in first die 20. A connectioncan be an electrical connection, for example with electrical conductorssuch as wires, an optical connection, for example with a light pipe suchas a fiber optic or photonic waveguide, or an opto-electronicconnection.

As shown in FIG. 9 and in step 140 of FIG. 1, each second die 22 can beconnected to a first die 20 after second die 22 is transfer printed tofirst die 20, for example with bond wires 80 connected to contact pads86 using wire bonding equipment. In some embodiments, each second die 22can be connected to a first die 20 after second die 22 is transferprinted to first die 20 by using photolithographic materials and methodsto form surface wires 82 (e.g., traces) with or with or without contactpads 86 on the respective surfaces of first and second dies 20, 22, asshown in FIG. 10. Referring to FIG. 11, in some embodiments, connectionposts 84 (e.g., spikes) connected to second integrated circuit 23 areformed in or on second dies 22. Connection posts 84 can extend from dies22 and can have a sharp point that pierces, penetrates, projects into,or otherwise electrically contacts contact pads 86 on first dies 20 toform an electrical connection 70 (shown in FIG. 13) between secondintegrated circuit 23 and first integrated circuit 21 when second die 22is transfer printed onto first die 20, for example by micro-transferprinting. In some such embodiments, the connection step 140 is the samestep as the transfer print step 130 and is illustrated as combined step135 in FIG. 1. Connection posts can require less space than, forexample, contact pads for wire bonding or surface wires 82 (shown inFIG. 10), and therefore enable reduced size of second dies 22, therebyreducing the cost and visibility of second dies 22, as well as reducingthe number of manufacturing steps required to combine and connect firstand second integrated circuits 21, 23 and construct compound die 60.

Referring to FIG. 12, after second dies 22 are transfer printed ontofirst dies 20 forming compound die 60, compound die 60 can be packaged(step 150, FIGS. 1 and 2) to construct a secure integrated-circuitsystem 99. Suitable ceramic and plastic integrated circuit packages(e.g., dual in-line packages or small-outline integrated circuitpackages), are widely available in the integrated-circuit industry andtypically comprise a package cavity 92 into which an integrated circuitis disposed and electrically connected with bond wires. According tosome embodiments, compound die 60 is disposed in or on, and optionallyadhered to, package 90, for example in package cavity 92, andelectrically connected to package leads 94, for example with packagebond wires 96 and contact pads 86, to provide connections from externaldevices to first and second integrated circuit 21, 23. In someembodiments, rather than connecting second integrated circuit 23 tofirst integrated circuits 21 before packaging (e.g., as in steps 140,135 in FIG. 1), second integrated circuits 23 are connected to firstintegrated circuits 21 after packaging (e.g., as in step 141, FIG. 2),for example with bond wires 80 (not shown between first and secondintegrated circuits 21, 23 in FIG. 12).

In some embodiments, second integrated circuit 23 is connected topackage 90 in a variety of different ways (e.g., by connecting contactpads 86 on second die 22 to contact pads on package 90, respectively).Such connections can directly enable connection to package leads 94 orconnect to first integrated circuit 21 through an additional connectionbetween package 90, package leads 94, and first die 20. Referring toFIG. 13, connections between multiple second dies 22 disposed on acommon first die 20 and the common first die 20 are made with connectionposts 84 (e.g., as shown in FIG. 13) and surface wires 82. Connectionsbetween first die 20 and package contact pads 86 are made with packagebond wires 96 to package contact pads 86. FIG. 14 illustrates bond wires80 directly connecting second dies 22. In FIG. 15, (package) bond wires80, 96 directly connect a second die 22 to a contact pad 86 on package90. Referring to FIGS. 13-15, although not shown, in some embodiments,package contact pads 86 are connected to package leads 94 (FIG. 12),providing an external connection to compound die 60.

In some embodiments, and as illustrated in FIG. 16, first and secondintegrated circuits 21, 23 are directly connected (e.g., as shown inFIGS. 9-11) with electrical connections 70, for example transmittingsignals through bond wires 80 (shown in FIG. 9), surface wires 82 (shownin FIG. 10), or connection posts 84 (shown in FIG. 11). First integratedcircuit 21 can be connected to external devices or systems throughinput/output signals 72 (as can second integrated circuit 23, althoughnot shown in FIG. 16), for example through package bond wires 96 andpackage leads 94. Second integrated circuit 23 can output monitor signal74, either directly through package bond wires 96 and package leads 94or indirectly through first die 20 or first integrated circuit 21.

In some embodiments, post processing (e.g., photolithographicprocessing) of first die 20 or compound die 60 is reduced by usingtransfer printing to construct compound die 60. Contact pads 86 on firstdie 20 can be left exposed, for example to enable wire bonding or toenable transfer printing to contact pads 86 (e.g., as shown FIG. 11).After compound die 60 is formed and first and second integrated circuits21, 23 are connected, it may only be necessary to provide anencapsulating layer to complete compound die 60. By minimizing postprocessing, additional processing expenses after first integratedcircuit 21 is completed can be reduced or obviated. By integrating firstand second dies 20, 22 into a single compound die 60, only a singlepackage 90 is needed which may further reduce size, manufacturing steps,and cost.

In operation, power is provided to first and second integrated circuit21, 23, for example through package leads 94. Second integrated circuit23 can receive power through first integrated circuit 21 or directlythrough package bond wires 96 and package leads 94 (e.g., as shown inFIG. 15). Once powered, first integrated circuit 21 operates and secondintegrated circuit 23 observes and monitors the operation of firstintegrated circuit 21. If an anomaly is detected, second integratedcircuit 23 provides a monitor signal 74 (e.g., as shown in FIG. 16) thatindicates anomalous operation. Monitor signal 74 can be provided on adedicated and direct connection, e.g., through a direct connectionbetween second integrated circuit 23 and a package lead 94 (e.g., asshown in FIG. 15). Monitor signal 74 can be provided through firstintegrated circuit 21 and a dedicated connection (e.g., as shown inFIGS. 13 and 14), or indirectly through one or more connections andpackage leads 94 that are used for other signals, as well.

In some embodiments, second die 22 is much smaller than first die 20.Such small dies can be transfer printed onto a surface of asemiconductor wafer or circuit and can be so small that they aredifficult to observe, providing additional security to a compound die60. For example, in some embodiments, first die 20 has an area that isat least ten (e.g., at least twenty, at least fifty, at least onehundred, at least two hundred and fifty, at least five hundred, at leastone thousand, at least five thousand, at least ten thousand, at leastone hundred thousand, at least one million, at least one hundredmillion, or at least one billion times) larger than an area of seconddie 22. In some embodiments, second die 22 has an area that is at leastten (e.g., at least twenty, at least fifty, at least one hundred, atleast two hundred and fifty, at least five hundred, at least onethousand, at least five thousand, at least ten thousand, at least onehundred thousand, at least one million, at least one hundred million, orat least one billion times) smaller than an area of first die 22. Insome embodiments, second die 22 can have a length and a width that areboth less than or equal to 200 microns, 100 microns, 50 microns, 25microns, or 10 microns. For example, first die 20 can have a length andwidth of ten centimeters (with an area of one hundred million squaremicrons) and second die 22 can have a length and width of 100 microns(with an area of ten thousand square microns) and an area ratio of tenthousand.

As discussed above, some methods comprise providing a plurality of firstdies 20, for example on a first destination wafer 40 (step 100),providing a plurality of second dies 22 (step 110), for example in asource wafer 10, and transfer printing only one second die 22 of theplurality of second dies 22 onto each first die 20 of the plurality offirst dies 20 (step 130). Some embodiments comprise transfer printingmultiple second dies 22 from a source wafer 10 to multiple first dies 20in a common step, with one second die 22 transfer printed to each firstdie 20. In some embodiments and as shown in FIG. 12, compound die 60comprises two or more second dies 22 and second integrated circuits 23.Multiple second dies 22 can be micro-transfer printed to a common firstdie 20, for example from different source wafers 10, with multiplerepetitions of transfer printing step 130. The multiple secondintegrated circuits 23 can be connected to provide a larger and morecomplex monitor circuit. Thus, some embodiments comprise providingmultiple source wafers 10 each having a plurality of second dies 22 andtransfer printing a second die 22 from each source wafer 10 onto acommon first die 20, so that each first die 20 has two or more seconddies 22 disposed thereon. Each second integrated circuit 23 on a commonfirst die 20 can be connected together to form a single monitor circuit.

According to some embodiments, a secure integrated-circuit system 99comprises a first integrated circuit 21 in a first die 20 having a firstdie size. The first integrated circuit can be constructed in an insecurefacility. A second integrated circuit 23 in a second die 22 has a seconddie size smaller than the first die size. The second integrated circuitcan be constructed in a secure facility. The second integrated circuit23 is operable to monitor the operation of the first integrated circuit21 and provides a monitor signal 74 responsive to the operation of thefirst integrated circuit 21. The second die 22 is transfer printed ontothe first die 20 and the second integrated circuit 23 is connected tothe first integrated circuit 21 to provide a compound die 60. Thecompound die 60 is disposed in a package 90. In some embodiments, thesecond die 22 comprises a fractured or separated tether.

In some embodiments, secure integrated-circuit system 99 comprise two ormore second dies 22 on a common first die 20. The two or more seconddies 22 are connected together to form a monitor circuit.

Transfer printing, for example micro-transfer printing, can includetransferring second dies 22 from a source substrate (e.g., source wafer10) to first dies 20 of a destination substrate (e.g., destination wafer40). Methods of micro-transfer printing can comprise contacting seconddies 22 on source wafer 10 with a stamp 30 to remove second dies 22 fromsource wafer 10, transferring stamp 30 and contacted second dies 22 tofirst dies 20 of destination wafer 40, and contacting second dies 22 toa surface of first dies 20 of destination wafer 40. Second dies 22 canbe adhered to stamp 30 or first dies 20 of destination wafer 40 by, forexample, van der Waals forces, electrostatic forces, magnetic forces,chemical forces, or adhesives. In some embodiments of the presentdisclosure, second dies 22 are adhered to stamp 30 withseparation-rate-dependent adhesion, for example kinetic control ofviscoelastic stamp materials such as can be found in elastomerictransfer devices such as a PDMS stamp 30. Stamps 30 can comprise stampposts 32 having a stamp post area on the distal end of stamp posts 32.Stamp posts 32 can have a length, width, or both length and width,similar or substantially equal to the length, width, or both length andwidth of second die 22. In some embodiments, stamp posts 32 are smallerthan second dies 22 in one or two orthogonal directions.

In exemplary methods, a viscoelastic elastomer (e.g., PDMS) stamp 30(e.g., comprising a plurality of stamp posts 32) is designed andfabricated to retrieve and transfer arrays of second dies 22 from theirnative source wafer 10 onto non-native destination wafers 40 or othernon-native destination substrates. Stamp 30 mounts ontomotion-plus-optics machinery (e.g., an opto-mechatronic motion platform)that can precisely control stamp 30 alignment and kinetics with respectto both source wafers 10 and destination wafers 40. Duringmicro-transfer printing, an opto-mechatronic motion platform bringsstamp 30 into contact with second dies 22 on source wafer 10, withoptical alignment performed before contact. Rapid upward movement of theprint-head and stamp 30 fractures second die 22 tether(s) 52 formingfractured tethers 53, transferring second die(s) 22 from source wafer 10to stamp 30 or stamp posts 32. The populated stamp 30 then travels todestination wafer 40 and one or more second dies 22 are then aligned todestination wafer 40 and printed on a surface of first die 20 ofdestination wafer 40.

In some embodiments, a source wafer 10 has releasable (e.g.,micro-transfer-printable) second dies 22 that can be transferred, forexample with a stamp 30. For example, a source wafer 10 can be asemiconductor (e.g., silicon in a crystalline or non-crystalline form orcrystalline silicon having a crystal structure of (1 0 0) or (1 1 1)), acompound semiconductor (e.g., comprising GaN or GaAs), or a glass,polymer, sapphire, or quartz wafer. Sacrificial portions 14 can beformed of a patterned oxide (e.g., silicon dioxide) or nitride (e.g.,silicon nitride) layer or can be an anisotropically etchable portion ofsacrificial layer 11 of source wafer 10. Typically, but not necessarily,source wafers 10 are smaller than destination wafers 40.

Second dies 22 can be any transfer printable structure, for exampleincluding a wide variety of active or passive (or active and passive)second dies 22 and can be or include any one or more of integrateddevices, integrated circuits (such as CMOS circuits), computers,communication equipment, light-emitting diodes, photodiodes, sensors,electrical or electronic devices, optical devices, opto-electronicdevices, magnetic devices, magneto-optic devices, magneto-electronicdevices, and piezo-electric device, materials or structures. Second dies22 can comprise electronic circuits that operate second die 22. Seconddies 22 can be responsive to electrical energy, to optical energy, toelectromagnetic energy, or to mechanical energy. For example, in someembodiments, second die 22 includes a light-emitting diode (LED), forexample to provide a monitor signal 74.

In some embodiments, second dies 22 formed or disposed in or on sourcewafers 10 can be constructed using one or more of integrated circuit,micro-electro-mechanical, and photolithographic methods. Second dies 22can comprise one or more different materials, for examplenon-crystalline or crystalline semiconductor materials such as siliconor compound semiconductor materials or non-crystalline or crystallinepiezo-electric materials.

In some embodiments of the present disclosure, second dies 22 are nativeto and formed on sacrificial portions 14 of source wafers 10 and caninclude seed layers for constructing crystalline layers on or in sourcewafers 10. Second dies 22, sacrificial portions 14, anchors 50, andtethers 52 can be constructed using photolithographic processes, forexample. Second dies 22 can be micro-devices having a length and/orwidth less than or equal to 200 microns, less than or equal to 100microns, less than or equal to 50 microns, less than or equal to 25microns, less than or equal to 15 microns, less than or equal to 10microns, or less than or equal to five microns, and, optionally, athickness of less than or equal to 50 microns, less than or equal to 25microns, less than or equal to 15 microns, less than or equal to 10microns, less than or equal to five microns, less than or equal to twomicrons, or less than or equal to one micron. Second dies 22 can beunpackaged dies (also referred to in the plural as dice, each anunpackaged die) transferred directly from native source wafers 10 on orin which second dies 22 are constructed to first dies 20 of destinationwafer 40. First dies 20 can be native to and formed on or in destinationwafers 40. Thus, second dies 22 can be non-native to destination wafers40. First dies 20 can be, but are not necessarily, transfer printable,having similar materials or structures as second dies 22 (e.g.,including fractured or separated tethers after transfer).

Anchors 50 and tethers 52 can each be or can each comprise portions ofsource wafer 10 that are not sacrificial portions 14 and can includelayers formed on source wafers 10, for example dielectric or metallayers and for example layers formed as a part of photolithographicprocesses used to construct or encapsulate second dies 22.

Destination wafer 40 can be any destination substrate or targetsubstrate, for example having first dies 20 disposed thereon to whichsecond dies 22 are transfer printed. For example, destination wafer 40can be a semiconductor wafer, flat-panel display substrate, printedcircuit board, or similar substrate. Destination wafers 40 can be, forexample substrates comprising glass, polymer, quartz, ceramics, metal,or sapphire. Destination wafers 40 can be semiconductor substrates (forexample silicon) or compound semiconductor substrates and can havemultiple layers.

In some embodiments of the present disclosure, a layer of adhesive, suchas a layer of resin, polymer, or epoxy, either curable or non-curable,adheres second dies 22 onto first dies 20 on destination wafer 40 andcan be disposed, for example by coating or lamination. In someembodiments, the layer of adhesive is disposed in a pattern, for exampleusing inkjet, screening, or photolithographic techniques. In someembodiments, a layer of adhesive is coated, for example with a spray orslot coater, and then patterned, for example using photolithographictechniques.

Patterned electrical conductors (e.g., wires, surface wires 82, bondwires 80, traces, or electrical contact pads 86, such as those found onsemiconductor wafers, printed circuit boards, flat-panel displaysubstrates, and in thin-film circuits) can be formed on any combinationof second dies 22, first dies 20, and destination wafer 40, and any onecan comprise electrical contact pads that electrically connect to seconddies 22. Such patterned electrical conductors (e.g., wires, surfacewires 82, bond wires 80) and contact pads 86 can comprise, for example,metal, transparent conductive oxides, or cured conductive inks and canbe constructed using photolithographic methods and materials. Forexample, metals such as aluminum, gold, or silver can be deposited byevaporation and patterned using pattern-wise exposed, cured, and etchedphotoresists, or constructed using imprinting methods and materials orinkjet printers and materials, for example comprising cured conductiveinks deposited on a surface or provided in micro-channels in or on firstdies 20 or destination wafer 40.

Micro-transfer printing processes and structures suitable for disposingsecond dies 22 onto first dies 20 of destination wafers 40 are describedin Inorganic light-emitting diode displays using micro-transfer printing(Journal of the Society for Information Display, 2017, DOI#10.1002/jsid.610, 1071-0922/17/2510-0610, pages 589-609), U.S. Pat. No.8,722,458 entitled Optical Systems Fabricated by Printing-BasedAssembly, U.S. patent application Ser. No. 15/461,703 entitled PressureActivated Electrical Interconnection by Micro-Transfer Printing, U.S.Pat. No. 8,889,485 entitled Methods for Surface Attachment of FlippedActive Components, U.S. patent application Ser. No. 14/822,864 entitledChiplets with Connection Posts, U.S. patent application Ser. No.14/743,788 entitled Micro-Assembled LED Displays and Lighting Elements,and U.S. Pat. No. 10,153,256, entitled Micro-Transfer PrintableElectronic Component, the disclosure of each of which is incorporatedherein by reference in its entirety.

For a discussion of micro-transfer printing techniques, see also U.S.Pat. Nos. 7,622,367 and 8,506,867, each of which is hereby incorporatedby reference in its entirety. Micro-transfer printing using compoundmicro-assembly structures and methods can also be used with the presentdisclosure, for example, as described in U.S. patent application Ser.No. 14/822,868, filed Aug. 10, 2015, entitled Compound Micro-AssemblyStrategies and Devices, which is hereby also incorporated by referencein its entirety. In some embodiments, micro-transfer printed structure99 is a compound micro-assembled structure (e.g., a macro-system).

According to various embodiments of the present disclosure, source wafer10 can be provided with second dies 22, patterned sacrificial portions14, tethers 52, and anchors 50 already formed, or they can beconstructed as part of a method in accordance with certain embodimentsof the present disclosure. Source wafer 10 and second dies 22,micro-transfer printing device (e.g., a stamp 30), and first dies 20 ofdestination wafer 40 can be made separately and at different times or indifferent temporal orders or locations and provided in various processstates.

The spatial distribution of any one or more of second dies 22 and firstdies 20 is a matter of design choice for the end product desired. Insome embodiments of the present disclosure, all second dies 22 in anarray on a source wafer 10 are transferred to a stamp 30 in a singletransfer. In some embodiments, a subset of second dies 22 in an array ona source wafer 10 is transferred in a single transfer. By varying thenumber and arrangement of stamp posts 32 on transfer stamps 30, thedistribution of second dies 22 on stamp posts 32 of the transfer stamp30 can be likewise varied, as can the distribution of second dies 22 onfirst dies 20 of destination wafer 40.

Because second dies 22, in certain embodiments, can be made usingintegrated circuit photolithographic techniques having a relatively highresolution and cost and destination wafer 40, for example a printedcircuit board, can be made using printed circuit board techniques havinga relatively low resolution and cost, electrical conductors and contactpads 86 on destination wafer 40 may be much larger than electricalcontacts or electrodes on second die 22 (or first dies 20), therebyreducing manufacturing costs. For example, in certain embodiments,micro-transfer printable second die 22 has at least one of a width,length, and height from 0.5 μm to 200 μm (e.g., 0.5 to 2 μm, 2 to 5 μm,5 to 10 μm, 10 to 20 μm, 20 to 50 μm, or 50 to 100 μm, or 100 to 200μm).

In certain embodiments, destination wafer 40 comprises a member selectedfrom the group consisting of polymer, plastic, resin, polyimide, PEN,PET, metal, metal foil, glass, a semiconductor, a compoundsemiconductor, and sapphire. In certain embodiments, destination wafer40 has a thickness from 5 microns to 20 mm (e.g., 5 to 10 microns, 10 to50 microns, 50 to 100 microns, 100 to 200 microns, 200 to 500 microns,500 microns to 0.5 mm, 0.5 to 1 mm, 1 mm to 5 mm, 5 mm to 10 mm, or 10mm to 20 mm).

First dies 20 and second dies 22, in certain embodiments, can beconstructed using foundry fabrication processes used in the art. Layersof materials can be used, including materials such as metals, oxides,nitrides and other materials used in the integrated-circuit art. Eachfirst die 20 or second die 22 can be or include a complete semiconductorintegrated circuit and can include, for example, one or more of atransistor, a diode, a light-emitting diode, and a sensor. Second dies22 can have different sizes, for example, 100 square microns or larger,1000 square microns, larger or 10,000 square microns or larger, 100,000square microns or larger, or 1 square mm or larger. Second dies 22 canhave variable aspect ratios, for example between 1:1 and 10:1 (e.g.,1:1, 2:1, 5:1, or 10:1). Second dies 22 can be rectangular or can haveother shapes. Likewise, first dies 20 can be rectangular and have a sizegreater than a size of second dies 22, for example having a size greaterthan 100,000 square microns, 1,000,000 square microns, 100,000,000square microns, or 1,000,000,000 square microns.

In some embodiments, transferring or transfer printing occurs bymicro-transfer-printing. In some embodiments, micro-transfer printinginvolves using a transfer device (e.g., an elastomeric stamp 30, such asa PDMS stamp 30) to transfer a second die 22 using controlled adhesion.For example, an exemplary transfer device can use kinetic orshear-assisted control of adhesion between a transfer device and asecond die 22. It is contemplated that, in certain embodiments, where amethod is described as including micro-transfer-printing a second die22, other analogous embodiments exist using a different transfer method.In some examples, transferring a second die 22 (e.g., from a sourcewafer 10 or wafer to a first die 20 of destination wafer 40) can beaccomplished using any one or more of a variety of known techniques. Forexample, in certain embodiments, a pick-and-place method can be used. Asanother example, in certain embodiments, a flip-chip method can be used(e.g., involving an intermediate, handle or carrier substrate). Inmethods according to certain embodiments, a vacuum tool or othertransfer device is used to transfer a second die 22.

As is understood by those skilled in the art, the terms “over” and“under” are relative terms and can be interchanged in reference todifferent orientations of the layers, elements, and substrates includedin the present disclosure. Furthermore, a first layer “on” a secondlayer is a relative orientation of the first layer to the second layerthat does not preclude additional layers being disposed therebetween.For example, a first layer on a second layer, in some implementations,means a first layer directly on and in contact with a second layer. Inother implementations, a first layer on a second layer includes a firstlayer and a second layer with another layer therebetween (e.g., and inmutual contact).

Throughout the description, where apparatus and systems are described ashaving, including, or comprising specific elements, or where processesand methods are described as having, including, or comprising specificsteps, it is contemplated that, additionally, there are apparatus andsystems of the disclosed technology that consist essentially of, orconsist of, the recited elements, and that there are processes andmethods according to the disclosed technology that consist essentiallyof, or consist of, the recited processing steps.

It should be understood that the order of steps or order for performingcertain action is immaterial so long as the disclosed technology remainsoperable. Moreover, two or more steps or actions in some circumstancescan be conducted simultaneously.

Having described certain implementations of embodiments, it will nowbecome apparent to one of skill in the art that other implementationsincorporating the concepts of the disclosure may be used. Therefore, thedisclosure should not be limited to certain implementations, but rathershould be limited only by the spirit and scope of the following claims.

PARTS LIST

-   A cross section line-   10 source wafer-   11 sacrificial layer-   14 sacrificial portions-   16 gap-   20 first die-   21 first integrated circuit-   22 second die-   23 second integrated circuit-   30 stamp-   32 stamp post-   40 destination wafer-   50 anchor-   52 tether-   53 fractured tether-   54 dielectric layer-   60 compound die-   70 electrical connection-   72 input/output signals-   74 monitor signal-   80 bond wires-   82 surface wires-   84 connection posts-   86 contact pad-   90 package-   92 package cavity-   94 package leads-   96 package bond wires-   99 secure integrated-circuit system-   100 provide first die step-   110 provide second die step-   120 provide package step-   130 transfer print second die onto first die step-   135 transfer print and connect second integrated circuit to first    integrated circuit step-   140 connect first integrated circuit to second integrated circuit    step-   141 connect first integrated circuit to second integrated circuit    step-   150 package compound die step

What is claimed is:
 1. A secure integrated-circuit system, comprising: afirst integrated circuit in a first die having a first die size; asecond integrated circuit in a second die having a second die sizesmaller than the first die size, wherein the second integrated circuitcomprises an electronic monitor circuit comprising transistors, whereinthe electronic monitor circuit is operable to monitor operation of thefirst integrated circuit and to provide a monitor signal responsive tothe operation of the first integrated circuit; and a fractured orseparated tether protruding from only a portion of a side of the seconddie, wherein the second die is non-native to the first die and thesecond integrated circuit is connected to the first integrated circuit,such that the first die and the second die together form a compound die,and wherein the compound die is disposed in a package.
 2. The secureintegrated-circuit system of claim 1, wherein the first die is a commonfirst die and comprising two or more second dies directly disposed onthe common first die, the two or more second dies connected together toform a monitor circuit.
 3. The secure integrated-circuit system of claim1, wherein the second integrated circuit does not comprise a maliciouscircuit.
 4. The secure integrated-circuit system of claim 1, wherein thefirst die has an area that is at least ten times larger than an area ofthe second die.
 5. The secure integrated-circuit system of claim 1,wherein the second die has a length and a width that are both no morethan 200 microns.
 6. The secure integrated-circuit system of claim 1,wherein the second integrated circuit is electrically connected to thefirst integrated circuit with at least one wire bond, at least onesurface wire, or at least one connection post.
 7. The secureintegrated-circuit system of claim 1, wherein the second integratedcircuit is connected to the first integrated circuit by one or more ofan electrical connection, an optical connection, and an electro-opticconnection.
 8. The secure integrated-circuit system of claim 1, whereinthe first integrated circuit comprises a malicious circuit.
 9. Thesecure integrated-circuit system of claim 1, wherein the second die isdisposed on or in contact with the first die.
 10. A secureintegrated-circuit system, comprising: a first integrated circuit in afirst die having a first die size; a second integrated circuit in asecond die having a second die size smaller than the first die size,wherein the second integrated circuit is operable to monitor theoperation of the first integrated circuit and to provide a monitorsignal responsive to the operation of the first integrated circuit; anda fractured or separated tether protruding from only a portion of a sideof the second die, wherein the second die is non-native to the first dieand the second integrated circuit is connected to the first integratedcircuit, such that the first die and the second die together form acompound die, wherein the compound die is disposed in a package.
 11. Thesecure integrated-circuit system of claim 10, wherein the second die isdisposed on or in contact with the first die.